Photovoltaic solar panels, also referred to simply as solar panels, comprise photovoltaic cells and can take any number of basic designs. One design employs crystalline silicon wafers connected together and embedded in a laminating film. The laminating film and the wafers embedded therein are typically sandwiched between two layers (or panels) of glass, a polymeric material or other suitable materials.
Another photovoltaic cell design employs one of amorphous silicon, cadmium-telluride (CdTe) or copper-indium-diselenide, CuInSe2 (commonly referred to as “CIS”), or a similar semiconductor material, which is deposited on a substrate in a thin film. These thin film photovoltaic materials are typically deposited in a thin film on a glass substrate by a method such as sputtering, Physical Vapor Deposition (“PVD”) or Chemical Vapor Deposition (“CVD”), and the photocells are typically formed by a laser etching process. To complete the construction, an assembly adhesive is applied over the photovoltaic material, associated circuitry, and any protective layer which is present, and a backing material is applied.
The circuitry, such as a bus bar, which collects the electrical current generated by the solar panel must be connected by wiring to a suitable storage device, such as a battery. The module wire must exit the solar panel at some point. Additional adhesive or sealant material is needed to seal around the module wire exiting the solar panel. The adhesive used for sealing around module wires may be the same as, or may differ from, the assembly adhesive used to attach the backing material to the solar panel.
Solar panels are used outdoors, and so are exposed to the elements, including wind, water and sunlight. Solar panels are deleteriously affected primarily by moisture which may permeate into the panel, reaching the electrical connections or the photovoltaic materials. Water penetration into solar panels has been a long-standing problem. Thus, various attempts have been made to reduce the moisture vapor transmission rate (MVTR). Solar panels may also be deleteriously affected by wind and sunlight, which may result in failure of the adhesive layer. Wind causes obvious physical damage, and sunlight results in heating of the solar panel and exposure to ultraviolet (UV) radiation. Thus, most all voltaic cells, photovoltaic cells in particular, are assembled with at least two encapsulant layers, one below and one above the cell, to provide moisture/oxygen/electrical isolation to the cell. In photovoltaic cells, at least one of the encapsulants that covers one face of the cell should be transparent. The cell will typically be formed on, or reside upon, the other encapsulant or “back sheet”, or may be formed or reside upon a so called “substrate” layer such as a metal or polyimide film that is then adjacent to the back sheet.
Many voltaic cell structures have been disclosed. Disclosures of interest include U.S. Pat. Nos. 5,508,205, 6,066,796, 6,420,646, 7,449,629, US 2008-0245405, US 2008-0276983, US 2009-0101204, US 2009-0162666 and WO 2007-002618. While there is some disclosure in the prior art of building solar panels having elastic components, there is still the practical problem of adhering all of the desired transparent and elastomeric layers together in a cost effect manner that still maintains the desired oxygen/moisture/electrical isolation for the photovoltaic cell.
Isobutylene-based elastomers are known to present extremely good barrier properties in certain applications. The inventors have found that isobutylene-based elastomers would allow for the fabrication of photovoltaic modules which are more impervious to moisture, while still being part of a flexible array. This class of materials can be formed into sheets by various methods, for example, calendering or blowing, and would be integrated into the manufacturing process of the module. Desirably, the isobutylene-based elastomers may act as both the back sheet for a cell assembly as well as an encapsulant.